Existing standards for human exposure to whole-body vibration are based heavily on data from experiments in which the vibration inputs were single sinusoids. An intensity matching technique was used to test the independent component method for evaluating complex vibration environments composed of multiple sine waves. Ten subjects adjusted the intensity of a 25 Hz sinusoid to match the subjective intensity of 11, 17, 40, and 63 Hz sinusoids (all with intensities at the same criterion level), presented either singly or in all possible combinations of two, three or four frequencies. The results showed a monotonic relationship between perceived intensity and the number of sinusoids in the stimulus (i.e., the acceleration of the matching response increased significantly as the number of sinusoids increased). These findings indicate (at least for the frequency range sampled) that the 'independent frequency' method of evaluating non-sinusoidal vibrations will underestimate the severity of such complex vibration environments.